This invention relates generally to means for heat removal from the fused quartz arc tube of an electric discharge lamp and more particularly, to such means being utilized for lamp operation at relatively high temperatures and discharge pressures.
Various high pressure type electric discharge lamps commonly employ a fused quartz arc tube as the light source by reason of the refractory nature and optical transparency of this ceramic material. In such type lamps the arc tube generally comprises a sealed envelope formed with fused quartz tubing with discharge electrodes being hermetically sealed therein. A typical arc tube construction hermetically seals a pair of discharge electrodes at opposite ends of the sealed envelope, although it is also known to have both electrodes being sealed at the same end of the arc tube. The sealed arc tube further contains a fill of various metal substances which becomes vaporized during the discharge operation to include mercury, sodium and metal halides along with one or more inert gases such as krypton, argon and xenon. Operation of such metal vapor discharge lamps can be carried out with various already known lamp ballasting circuits employing both alternating current and direct current power sources. High luminous efficacy is achieved with these type metal vapor lamps with the new lamp designs increasing such efficacy by increasing discharge pressures while also reducing lamp envelope size.
Lot spot wall temperatures of about 1000.degree. C. are frequently reached by the quartz arc tube in such lamps at the relatively high operating temperatures and pressures being employed. The fused quartz material can undergo rapid diversification or crystallization in such pressurized thermal environment thereby seriously limiting lamp life by rupture. Upon such an occurrence, the high pressure within a lamp may further cause materials from the quartz tube to become further dislodged at a relatively high velocity possibly fracturing even the outer housing means for the lamp such as employed in an automotive headlamp application. In product applications wherein the quartz arc tube is positioned within a reflector member, such as in automotive headlamps and still other product applications, any bulging of the arc tube caused by exposure to such elevated pressure and temperature conditions can adversely affect the desired illumination pattern. There is a serious need, therefore, to reduce hot spot wall temperatures being experienced during lamp operation.
Accordingly, it is an object of the present invention to provide means to remove heat from a fused quartz arc tube being employed in an electric discharge lamp.
Another object of the present invention is to provide an electric discharge lamp employing a fused quartz arc tube which includes particular heat transfer means operatively associated with said arc tube to remove heat being conducted through the arc tube walls.
Still a further object of the present invention is to utilize a fused quartz medium for heat removal from an electric discharge lamp.
It is a still further object of this invention to provide an automotive headlamp employing a fused quartz arc tube as the light source which includes heat removal means operatively associated with said arc tube.
These and other object of the present invention will become apparent upon considering the following more detailed description.